The speed limit posted on a road is 55 mph. when the road is wet:

45 miles per hour

If the posted speed limit is 55 mph, then you should travel at least 10 miles slower when the road is wet. Though state laws vary, most agree that you should drive at least 5-10 miles slower than the posted speed limit. Just to be on the safe side, always travel 10 miles slower than the posted speed limit when the roads are wet.